<template>
  <div class="slider" ref="slider">
    <div class="slider-group" ref="sliderGroup">
      <slot></slot>
    </div>
    <div class="dots">
      <span class="dot" v-for="(item,index) in dots" :key="index" :class="{active:currentPageIndex===index}"></span>
    </div>
  </div>
</template>

<script type="text/ecmascript-6">
import BScroll from 'better-scroll'
import { addClass } from '@/assets/js/dom.js'
export default {
  name: 'slider',
  props: {
    loop: {
      type: Boolean,
      default: true
    },
    autoPlay: {
      type: Boolean,
      default: true
    },
    interval: {
      type: Number,
      default: 4000
    }
  },
  data() {
    return {
      dots: [],
      currentPageIndex: 0
    }
  },
  mounted() {
    // 浏览器刷新通常是17毫秒
    // setTimeout(() => {
    //   this._setSliderWidth()
    //   this._initDots()
    //   this._initSlider()
    //   // 自动播放
    //   // if(this.autoPlay){
    //   //   this._play()
    //   // }
    // }, 20)
    this.$nextTick(() => {
      this._setSliderWidth()
      this._initDots()
      this._initSlider()
    })
  },
  destroyed() {
    clearTimeout(this.timer)
  },
  methods: {
    _setSliderWidth() {
      this.children = this.$refs.sliderGroup.children
      let width = 0
      let sliderWidth = this.$refs.slider.clientWidth
      for (let i = 0; i < this.children.length; i++) {
        let child = this.children[i]
        addClass(child, 'slider-item')
        child.style.width = sliderWidth + 'px'
        width += sliderWidth
      }

      if (this.loop) {
        width += 2 * sliderWidth
      }
      this.$refs.sliderGroup.style.width = width + 'px'
    },
    _initDots() {
      this.dots = new Array(this.children.length)
    },
    _initSlider() {
      this.slider = new BScroll(this.$refs.slider, {
        scrollX: true,
        scrollY: false,
        autoPlay: false,
        // 惯性 当快速在屏幕上滑动一段距离的时候，会根据滑动的距离和时间计算出动量
        momentum: false,
        slide: {
          loop: this.loop,
          threshold: 0.3,
          speed: 400
        },
        snapSpeed: 400,
        click: true
      })
      this.slider.on('scrollEnd', () => {
        // console.log(this.slider)
        // console.log(this.slider.getCurrentPage())
        let pageIndex = this.slider.getCurrentPage().pageX
        // better-scroll版本更新，下面的if不需要了
        // if (this.loop) {
        //   // pageIndex -= 1
        // }

        // 获取索引
        this.currentPageIndex = pageIndex
      })
    }
  }
}
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
@import '~@/assets/stylus/variable';

.slider {
  min-height: 1px;

  .slider-group {
    position: relative;
    overflow: hidden;
    white-space: nowrap;

    .slider-item {
      float: left;
      box-sizing: border-box;
      overflow: hidden;
      text-align: center;

      a {
        display: block;
        width: 100%;
        overflow: hidden;
        text-decoration: none;
      }

      img {
        display: block;
        width: 100%;
      }
    }
  }

  .dots {
    position: absolute;
    right: 0;
    left: 0;
    bottom: 12px;
    text-align: center;
    font-size: 0;

    .dot {
      display: inline-block;
      margin: 0 4px;
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: $color-text-l;

      &.active {
        width: 20px;
        border-radius: 5px;
        background: $color-text-ll;
      }
    }
  }
}
</style>